Many saline minerals are recognized as being commercially valuable. For example, trona, borates, potash and sodium chloride are mined commercially. After mining, these minerals typically need to be beneficiated to remove naturally occurring impurities.
With regard to trona (Na.sub.2 CO.sub.3.NaHCO.sub.3.2H.sub.2 O), high-purity trona is commonly used to make soda ash, which is used in the production of glass and paper. Naturally-occurring trona, or crude trona, is found in large deposits in the western United States, such as in Wyoming and California, and also in Egypt, Kenya, Botswana, Tibet, Venezuela and Turkey. Crude trona ore from Wyoming is typically between about 80% and about 94% trona, with the remaining components including shortite, halite, quartz, dolomite, mudstone, oil shale, kerogen, mica, nahcolite and clay minerals.
The glass and paper making industries generally require soda ash produced from trona having a purity of 99% or more. In order to obtain such a high purity, beneficiation processes including dissolution and recrystallization have been used. For example, crude trona can be calcined to yield anhydrous sodium carbonate, which is then solubilized, treated to remove impurities, crystallized and dried to produce sodium carbonate monohydrate. Calcination of trona produces both gas and particulate pollutants which are released into the atmosphere.
Other wet beneficiation processes, such as those disclosed in U.S. Pat. No. 5,396,863 and U.S. Pat. No. 2,887,360, disclose methods and/or apparatus for treating non-trona forms of sodium carbonate. For example, U.S. Pat. No. 5,396,863 discloses a method for treating non-trona forms of sodium carbonate by a densification process. In this regard, U.S. Pat. No. 5,396,863 is suitable for the production of dense anhydrous sodium carbonate (usually referred to as dense soda) from light anhydrous sodium carbonate (usually referred to as light soda). U.S. Pat. No. 2,887,360 discloses purification of impure sodium carbonate, such as from the ammonia-soda process, which is contaminated with an impurity, such as boron compounds, silica compounds and/or sulfates. This process includes introducing sodium carbonate to a super-saturated slurry, heating the slurry above the transition temperature (about 112.degree. CC) to anhydrous sodium carbonate and cooling to form monohydrate sodium carbonate crystals. Solids are then removed from the slurry to separate the crystals from soluble impurities.